Three-phase reluctance type motor

ABSTRACT

The present invention relates to a three-phase reluctance type motor with a large output torque which can be used as a driving source of various industrial apparatus. There are provided adjacent two magnetic poles (16a, 16a&#39;) and other adjacent two magnetic poles (16d, 16d&#39;) facing to above adjacent two magnetic poles in a diameter direction of the motor with relation to each of first to third phases. These four magnetic poles are excited by four exciting coils (17a, 17a&#39;, 17d, and 17d&#39;), respectively. The exciting coils of each phase generates a large magnetomotive force as a whole. In such a manner, a limited installation space for the exciting coil is effectively utilized so as to increase magnetomotive force of the exciting coil, thus a large output torque is generated. Furthermore, at the moment the current supply to respective phase exciting coil (17a, 17a&#39;, 17d, and 17d&#39;) is terminated, magnetic energy stored in one phase exciting coil is transferred into other phase exciting coil (17a, 17a&#39;, 17d, and 17d&#39;), thereby promptly extinguishing the stored magnetic energy stored in the one phase exciting coil and promptly building up an exciting current in the other phase exciting coil so that the motor can be driven in a high speed region.

TECHNICAL FIELD

The present invention relates to a reluctance type motor, particularlyto a three-phase reluctance type motor capable of outputting largetorque and preferable for using as driving sources for variousindustrial apparatus.

BACKGROUND ART

Typical three-phase reluctance type motor comprises a stator having sixmagnetic poles and a rotor having four or eight salient-poles. Threesets of magnetic poles, each set consisting of two magnetic poles facingeach other in a diameter direction of the motor, are associated withthree sets of exciting coils constituting a first to a third phaseexciting coils, respectively. When exciting current is successivelysupplied to the first to the third exciting coils, the magnetic polesare excited to cause magnetic attraction force between the excitedmagnetic poles and their corresponding salient-poles. And, this magneticattraction force causes the rotor to rotate.

In a reluctance type motor, even when a magnetic flux penetratingmagnetic poles is in a saturated condition, an output torque of themotor increases in accordance with increase of a magnetomotive force(i.e. an ampere-turn) defined by a number of turns of an exciting coilmultiplied by its exciting current. For example, in case of a reluctancemotor of approximately 500 watt output, as shown in FIG. 1, an outputtorque increases in proportion to a square value of an exciting currentin a region 3a in which the exciting current is smaller than, forexample, 2 ampere, and to the contrary it increases in proportion to theexciting current itself in a region 3b in which the exciting current islarger than 2 ampere.

Accordingly, theoretically, the output torque of motor can be increasedby increasing magnetomotive force of exciting coils. However, anavailable space inside of the motor which the exciting coils can occupyis limited, therefore it is difficult to scale up the exciting coil inorder to increase number of turns of the exciting coil. Furthermore, anincrease of the exciting current is accompanied with increase of copperloss. Thus, it is difficult to increase an output torque of thereluctance type motor by increasing magnetomotive force of the excitingcoil.

Generally, in a three-phase reluctance type motor, an initiation and atermination of exciting current supply coincides with a 180-degreeelectric angle rotation of a rotor. That is, during one completerevolution of the rotor, an accumulation and an extinction of magneticflux are repeated 6 times. Such a large number of repetition of theaccumulation and the extinction of magnetic flux during one completerevolution of the rotor increases iron loss in the reluctance typemotor. Moreover, since an inductance of the exciting coil is large,magnetic energy stored in the exciting coil becomes remarkably large.Therefore, it requires significant time for completion of accumulationand extinction of magnetic energy. For this reason, a building-up and atrailing edge of the exciting current are delayed undesirably.

Accordingly, not only torque reductions occur (i.e. the torque isreduced), but also counter torques are generated. However, since thesetorque reduction and counter torque generation are increased inaccordance with increase of rotational speed of the motor, it isdifficult to cause the motor to rotate in a high speed region.

Especially, if the number of salient-poles and magnetic poles isincreased in order to increase an output torque of the motor, or a gapbetween the salient-pole and the magnetic pole is set to be small, aperiod of time required for the building-up or the trailing edge of theexciting current derived from stored magnetic energy further increases.Thus, the rotational speed remarkably decreases.

Consequently, in a conventional reluctance type motor, it was difficultto realize both a required rotational speed and a large output torque.

SUMMARY OF INVENTION

The purpose of the present invention is to provide a three-phasereluctance type motor of large output torque which can be used asdriving sources for various industrial apparatus.

In order to accomplish the above purpose, a three-phase reluctance typemotor of the present invention comprises: a fixed armature with threesets of magnetic poles relating to first, second, and third phases whichare formed on its inner peripheral surface according to a predeterminedorder; three sets of exciting coils being associated with the three setsof magnetic poles and relating to the first, the second, and thirdphases; and a rotor which is rotatably disposed and has an outerperipheral surface formed with a predetermined number of salient-polesdisposed at regular intervals, said predetermined number exceeding atotal number of magnetic poles of the fixed armature.

Each set of magnetic poles consists of adjacent two magnetic poles andother adjacent two magnetic poles facing the adjacent two magnetic polesin a diameter direction of the motor. And, each set of exciting coilsare connected with each other.

Furthermore, a three-phase reluctance type motor in accordance with thepresent invention comprises: a position detecting device forsuccessively generating a series of position detecting signals inaccordance with rotation of the rotor; a current supply control circuitbeing connected to a direct-current power source for successivelyactivating three sets of exciting coils in response to the positiondetecting signals; and a circuit means which discharges magnetic energystored in one set of exciting coils having been just deactivated intoanother set of exciting coils to be subsequently activated so that notonly the stored magnetic energy can be promptly extinguished but anexciting current flowing in another set of exciting coils can be steeplyincreased.

As described above, in accordance with the present invention, fourmagnetic poles consisting of adjacent two magnetic poles and otheradjacent two magnetic poles facing the above adjacent two magnetic polesin a diameter direction of the motor are provided in conjunction witheach of the first, the second, and the third phases. These four magneticpoles are excited by four exciting coils associated with these magneticpoles respectively. As a result, an overall magnetomotive force ofexciting coils of respective phases is largely increased compared with aconventional reluctance type motor which is provided with two excitingcoils relating to each of a first, a second, and a third phases.

Namely, in accordance with the present invention, a limited installationspace for exciting coils inside of the motor is effectively utilized.Accordingly, a magnetomotive force of exciting coils can be increasedwithout scaling up the motor, and therefore the output torque of themotor can be increased.

Further, in accordance with the present invention, magnetic energystored in one set of exciting coils having been just deactivated isdischarged into another set of exciting coils to be subsequentlyactivated, therefore not only the stored magnetic energy can be promptlyextinguished but the exciting current flowing in another set of excitingcoils can be steeply increased.

Consequently, a motor in accordance with the present invention can bedriven at a higher rotational speed which is required as a drivingsource for various industrial apparatus, irrespective of the increasednumber of magnetic poles and salient-poles compared with conventionalmotors. In this manner, the present invention provides a three-phasereluctance type motor of large output torque capable of being used as adriving source suitable for various industrial apparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph exemplarily showing a curve representing arelationship between an exciting current value and an output torquevalue in a reluctance type motor;

FIG. 2 is a schematic cross-sectional view showing a main body of athree-phase half-wave reluctance type motor in accordance with a firstembodiment of the present invention;

FIG. 3 is a development showing a rotor and an armature of FIG. 2together with position detecting elements about a half peripheralportion of the motor;

FIG. 4 is a schematic circuit diagram showing a position detectingdevice adopted together with a motor main body;

FIG. 5 is a schematic circuit diagram showing a current supply controlcircuit used together with the motor main body and the positiondetecting device;

FIG. 6 is a graph showing exciting current curves and output torquecurves;

FIG. 7 is a timing chart showing changes of various signals in theposition detecting device with respect to elapsed time;

FIG. 8 is a partly shown schematic cross-sectional view of a modifiedembodiment of magnetic poles different from the magnetic poles of thefirst embodiment in its cross-sectional configuration;

FIG. 9 is a development, which is similar to FIG. 3, showing a modifiedembodiment of the motor main body having a different number ofsalient-poles compared with that of the first embodiment; and

FIG. 10 is a schematic circuit diagram showing a current supply controlcircuit in accordance with a second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A three-phase half-wave reluctance type motor in accordance with a firstembodiment of the present invention comprises a motor main body shown inFIG. 2. The motor main body comprises a surrounding wall 23 of ahousing, a rotor shaft 5 with its end portions being rotatably supportedon bearings (not shown) provided on both end walls of the housing whichare respectively fixed to the surrounding wall 23 of the housing, arotor 1 coupled with the rotor shaft 5, and an armature (i.e. a stator)16 disposed coaxially with the rotor 1 and fixed on the surrounding wall23 of the casing.

The rotor 1 and the armature 16 are respectively made of a well-knownlamination layer of silicon steel sheet. The housing surrounding wall 23is buried and fixed in an outer peripheral surface of the armatureformed with recessed portions 24a to 24f by an aluminum die-cast. Adie-cast material constituting the surrounding wall 23 intrudes in anouter peripheral portion of the armature 16 by a depth indicated by aletter E in the drawing. Connecting portions 24a' to 24f' between thesurrounding wall 23 and the armature 16 are removed by being cut afterhaving finished the die-cast work. That is, on the armature 16, thereare formed with cutouts 24a' to 24f' partitioning a magnetic pathrelating to one adjacent pair of magnetic poles from a magnetic pathrelating to other adjacent pair of magnetic poles.

On outer peripheral surface of the rotor 1, twenty six salient-poles 1ato 1z each having the same circumferential width are formed at regularintervals in a circumferential direction so as to respectively protrudein a radially outward direction. Moreover, the armature 16 has acircular magnetic core 16' freely forming a magnetic path, and twelvemagnetic poles 16a to 16f and 16a' to 16f' are formed at regularintervals in a circumferential direction on an inner peripheral surfaceof the magnetic core so as to respectively protrude in a radially inwarddirection. Tip (i.e. distal) ends of the magnetic pole and its opposingsalient-pole are disposed to face with each other over an air gap of anapproximately 0.15 mm. The magnetic poles have respectively the samecircumferential width, which is the same width as that of thesalient-pole. A spaced gap of adjacent two magnetic poles, for example,magnetic poles 16a and 16a', coincides with a section wherein threesalient-poles, for example, salient-poles 1a to 1c are disposed. Thatis, adjacent two magnetic poles are spaced with each other by a distanceequal to four times of a width of salient-pole.

The adjacent two magnetic poles 16a, 16a' constitute a first set ofmagnetic poles together with adjacent two magnetic poles 16d, 16d' whichare disposed to oppose above adjacent two magnetic poles 16a, 16a' in adiameter direction of the motor. The first set of magnetic poles relatesto a first phase. The adjacent two magnetic poles 16b, 16b' constitute asecond set of magnetic poles together with adjacent two magnetic poles16e, 16e' which are disposed to oppose above adjacent two magnetic poles16b, 16b' in a diameter direction of the motor. The second set ofmagnetic poles relates to a second phase. And, the adjacent two magneticpoles 16c, 16c' constitute a third set of magnetic poles together withadjacent two magnetic poles 16f, 16f' which are disposed to oppose aboveadjacent two magnetic poles 16c, 16c' in a diameter direction of themotor. The third set of magnetic poles relates to a third phase.

These magnetic poles 16a to 16f and 16a' to 16f' are associated withexciting coils 17a to 17f and 17a' to 17f', respectively. Since adjacenttwo magnetic poles are spaced with each other by a distance equal tofour times of a width of salient-pole, there is provided a fairly largeoccupying space for the exciting coils to be coupled with the magneticpoles. Accordingly, it becomes possible to constitute each exciting coilby turning a large diameter copper wire by a required turn number so asto obtain a required magnetomotive force.

The first set of exciting coils 17a, 17a', 17d, and 17d' relating to thefirst phase are connected with each other in series or in parallel.Otherwise, the first set of exciting coils 17a, 17a', 17d, and 17d' areconnected in such a manner that two pair of series exciting coils areconnected in parallel. Hereinafter, this connected unit is referred toas a first phase exciting coil K. The second set of exciting coils 17b,17b', 17e, and 17e' and the third set of exciting coils 17c, 17c', 17f,and 17f' are connected in the same fashion as the first set of excitingcoils 17a, 17a', 17d, and 17d'. These connected units are referred to asa second phase exciting coil L and a third phase exciting coil M.

The motor comprises a position detecting device shown in FIG. 4. Theposition detecting device includes three detecting elements 10a to 10c(FIG. 3) each consisting of an air-core coil of approximately 100 turnshaving 5 mm diameter for detecting rotational positions of salient-poles1a to 1z of the rotor 1. These detecting elements (hereinafter, referredto as detecting coils) are respectively spaced by 120 degrees with eachother, and respective coil surface are fixed on the armature 16 so as toface the side surfaces of the salient-poles 1a to 1z with keeping airgaps. Furthermore, the position detecting device includes an oscillator7 having an oscillation frequency of approximately 1 MHz. An output ofthe oscillator 7 is connected to a bridge circuit consisting ofdetecting coils 10a to 10c and resistance 15a to 15e.

This bridge circuit is adjusted to balance in a condition that thedetecting coils 10a to 10c do not face to any of the salient-poles 1a to1z. This bridge circuit is connected to a logic circuit 8 throughlow-pass filters consisting of diodes 11a to 11d and capacitors 12a to12d and operational amplifiers 13a to 13c.

In more detail, the diode 11a has an anode connected to the connectingpoint of the coil 10a and the resistance 15a, and has a cathodeconnected to both the other end of the capacitor 12a with one end beinggrounded and the positive input terminal of the operational amplifier13a. In a similar way, the diode 11b has an anode connected to theconnecting point of the coil 10b and the resistance 15b and has acathode connected to both the other end of the capacitor 12b with oneend being grounded and the positive input terminal of the operationalamplifier 13b. And further, the diode 11c has an anode connected to theconnecting point of the coil 10c and the resistance 15c and has acathode connected to both the other end of the capacitor 12c with oneend being grounded and the positive input terminal of the operationalamplifier 13c.

And, the diode 11d has an anode connected to the connecting point ofresistances 15d, 15e and has a cathode connected to both the other endof the capacitor 12d with one end being grounded and negative inputterminals of the operational amplifiers 13a to 13c. Output terminals ofthe operational amplifiers 13a to 13c are connected to input terminalsof the logic circuit 8.

The motor further comprises a current supply control circuit shown inFIG. 5 to allow or prevent the exciting current supply to the excitingcoils 17a to 17f and 17a' to 17f'; i.e. the first to third phaseexciting coils K to M.

Input terminals 4a to 4c of the current supply control circuit areconnected, on one hand, to output terminals 6a to 6c of the positiondetecting device, and connected, on the other hand, to one side inputterminals of AND circuits 14a to 14c of the current supply controlcircuit, respectively. And, the other side input terminals of the ANDcircuits 14a to 14c are connected to a standard voltage input terminal40 to which a standard voltage is applied in order to vary an outputtorque of the motor, through an operational amplifier 40a constituting alater-described chopper circuit together with the AND circuits.

Further, output terminals of the AND circuits 14a to 14c are connectedthrough inversion circuits to bases of transistors (i.e. switchingelements) 20a, 20c, and 20e interposed between a positive terminal 2a ofthe DC power source and one end of the first to third phase excitingcoils K to M. The other ends of the first to third phase exciting coilsK to M are connected through transistors 20b, 20d, 20f and resistance 22to a negative terminal 2b of the DC power source, and on the other hand,connected through transistors 20b, 20d, and 20f to a negative terminalof the operational amplifier 40a.

The resistance 22 is provided to detect an exciting current flowing inthe first to third phase exciting coils K to M. One end of theresistance 22 is connected to emitters of the transistors 20b, 20d, and20f, and the other end is connected to anodes of diodes 21a, 21c, and21f. Cathodes of these diodes 21a, 21c, and 21f are connected to oneside end of the first to third phase exciting coils K to M. And further,diodes 21b, 21d, and 21f are interposed between the other side ends ofthe first to third phase exciting coils K to M and the positive terminal2a of the DC power source.

Hereinafter, an operation of three-phase half-wave reluctance typemotor, constituted as above-described, will be explained in thefollowing.

The bridge circuit of the position detecting device (FIG. 4) installedin the motor is adjusted to balance when the detecting coils 10a to 10cdo not face any one of the salient-poles 1a to 1z of the rotor 1.Accordingly, when the detecting coil 10a does not face any one of thesalient-poles 1a to 1z, an output of the low-pass filter consisting ofthe diode 11a and the capacitor 12a becomes equal to an output of thelow-pass filter consisting of the diode 11d and the capacitor 12d.Therefore, an output of the operational amplifier 13a becomes aLOW-level. However, as a matter of fact, when the motor is stopped, anyone of the detecting coils faces to any one of salient-poles.

Accordingly, for example in the case that the detecting coil 10a facesany one of salient-poles, impedance of the detecting coil 10a decreasesdue to core loss (i.e. eddy loss and hysteresis loss). Therefore,voltage drop in the resistance 15a becomes large, and an applied voltageto the positive input terminal of the operational amplifier 13aincreases to turn the output 25 of the operational amplifier into aHIGH-level (as indicated by the reference numerals 25a, 25b in FIG. 7).That is, in accordance with rotation of the rotor 1, rectangular-wavesignals 25 are sent out from the operational amplifier 13a.

When each of the detecting coils 10b, 10c faces to the side surface ofany one of salient-poles 1a to 1z, voltage drops at the resistances 15b,15c become large. Therefore, input voltages, applied through thelow-pass filters 11b, 12b and 11c, 12c, increases to turn the output 26,27 (FIG. 7) of the operational amplifiers 13b, 13c into a HIGH-level (asindicated by the reference numerals 26a, 26b, 27a, and 27b in FIG. 7).And, in accordance with the rotation of the rotor 1, rectangular-wavesignals 26, 27 are output from both operational amplifiers. The aboverectangular-wave signals 25 to 27 have a phase difference of 120 degreeswith respect to each other.

The logic circuit 8 has input terminals inputting these rectangular-wavesignals 25 to 27 and outputting rectangular-wave signals 28 to 30 (FIG.7) corresponding to an AND result of mutually corresponding ones amongthe rectangular-wave signals 25, 26 and 27 and their inverted signals.As a result, in accordance with rotation of the motor, output terminals6a to 6c of the position detecting device successively send out first tothird position detecting signals 28 to 30 (FIG. 7) of 120-degree widthwhich relate to the first to third exciting coils K to M and representpositions of salient-poles of the rotor 1.

When the motor is turned on, electric current is supplied from thepositive and negative terminals 2a, 2b of the DC power source in thecurrent supply circuit (FIG. 5). Furthermore, a negative input terminalof the operational amplifier 40a is applied to a voltage lower than avoltage applied to its positive input terminal. A HIGH-level signal isapplied from the operational amplifier 40a to the AND circuits 14a to14c to open the gates of these AND circuits. As is described above, whenthe motor is started, any one of the detecting coils 10a to 10c of theposition detecting device faces any one of the salient-poles 1a to 1z ofthe rotor 1 of the motor.

In such a condition, for example, when the second phase positiondetecting signal 29a of a HIGH-level is applied from the positiondetecting device to an input terminal 4b of the current supply controlcircuit, this HIGH-level signal 29a is applied to the base of thetransistor 20d. And, a HIGH-level output sent out from the AND circuit14b, of which gate is in an opened condition, is converted into aLOW-level output through the inversion circuit and, in turn, applied tothe base of the transistor 20c. Accordingly, the transistors 20c, 20dare activated to turn on the second phase exciting coil L.

As a result of these changes, magnetic poles 16b and 16b' of thearmature 16 are magnetized to become an N-pole and an S-pole,respectively, and the magnetic poles 16e and 16e' of the armature 16 aremagnetized to become an N-pole and an S-pole, respectively. Accordingly,the salient-poles 1e, 1g, 1r, and 1t are attracted by magnetic force tocause the rotor 1 to rotate in a direction A of FIG. 2. After that, ifthe rotor 1 rotates 120 degrees, the second phase position detectingsignal 29 becomes a LOW-level and, at the same time, the third phaseposition detecting signal 30a of a HIGH-level is applied to the inputterminal 4c of current supply control circuit. Namely, the second phaseexciting coil L is deactivated and the third phase exciting coil M isactivated.

If, the rotor 1 further rotates 120 degrees, the third phase excitingcoil M is deactivated and the first phase exciting coil K is activated.

In such a manner, current supply mode is cyclically alternated atintervals of 120-degree revolutions as follows; the first exciting coilK, the second exciting coil L, the third exciting coil M. As a result,the exciting coils K to M are successively and continuously suppliedexciting current to cause the motor to generate output torque.

During the current supply operation to each of the first to third phaseexciting coils K to M, a magnetic path relating to each pair of twopairs of exciting coils, which are in excited condition, is closed asindicated by a broken line F in FIG. 2, since the armature 16 is formedwith cutouts 24a' to 24f' having a function of partitioning a magneticpath. Therefore, during the current supply period of time to respectivephase exciting coils, magnetic flux generated by the exciting coilspasses only a portion of armature which contributes to generate torqueand does not pass other portions. Namely, the magnetic poles of eachphase have substantially the same construction as an U-shaped magneticcore. Consequently, the exciting current is effectively utilized togenerate torque and also to reduce copper loss. Furthermore, since anoverall volume of a magnetic member becomes minimum, an efficiency ofthe motor can be increased due to reduction of core loss. The core lossoccurs in accordance with generation of magnetic flux or its extinctionwhich is related to an initiation or termination of current supply tothe exciting coils.

Moreover, during a current supply period of time to respective excitingcoils K, L, or M, excited two pairs of magnetic poles generate amagnetic attraction force acting in a radial direction in addition to amagnetic attraction force acting in a circumferential direction.However, the radial magnetic attraction force generated by one pair ofmagnetic poles and the radial magnetic attraction force generated by theother pair of magnetic poles are mutually canceled, thereby preventingdamage of bearings and suppressing occurrence of vibration.

During a current supply period of time to respective phase excitingcoils, for example, during the first phase position, detecting signal28a of a HIGH-level is generated to activate the first phase excitingcoil K. If exciting current flowing in the exciting coil K exceeds a setvalue corresponding to the standard voltage, which is applied to thepositive input terminal of the operational amplifier 40a through thestandard voltage input terminal 40 in the current supply control circuitof FIG. 5 and is set variably, an output of the operational amplifierbecomes a LOW-level and the gate of the AND circuit 14a closes so as todeactivate the transistor 20a.

In this instance, magnetic energy stored in the exciting coil K isdischarged as current flowing through the diode 21a, the transistor 20b,and the resistance 22. Subsequently, when this discharge current reducesdown to a predetermined value to be determined in accordance with ahysteresis characteristic of the operational amplifier 40a, the outputof the operational amplifier returns to a HIGH-level so as to activatethe transistor 20a again to let exciting current flow.

In this manner, the operational amplifier 40a cooperates with the ANDcircuit 14a to activate or deactivate the transistor 20a on the basis ofcomparison between the exciting current and above set value so as tocontrol the exciting current; i.e. the output torque of the motor. Thesame explanation is applied to other phases. Thus, the operationalamplifier 40a functions as a chopper circuit together with the ANDcircuits 14a to 14c.

Next, referring now to FIG. 6, the following is an explanation ofcharacteristic features in the operation of the motor in accordance withthe present embodiment.

In a conventional motor, for example, if the exciting current issupplied to the second phase exciting coil L during a sectioncorresponding to a 120-degree width of the second phase positiondetecting signal 29a shown by an arrow 36, the exciting current causes atime lag in its building-up state as shown by a first half of a brokenline curve 35 due to large inductance of the exciting coil L.

Moreover, since large magnetic energy is discharged, a trailing edge ofthe exciting current is extended as shown by a second half of the curve35. Hereupon, an arrow 36b denotes a 180-degree section during which apositive torque is generated. Accordingly, the torque decreases duringthe first half of the curve 35 (hereinafter, referred to as a generationof torque reduction). On the other hand, a large counter torque isgenerated during the last half. Thus, a conventional motor has a lowefficiency, and its rotational speed is low.

In accordance with the motor of the present embodiment, such adisadvantage can be removed. The reason is explained as follows. Forexample, when the exciting current is supplied to the second phaseexciting coil L in accordance with the second position detecting signal29a, a high voltage is applied from the DC power source 2a. Thus, theexciting current increases steeply as shown by a broken line curve 35bin FIG. 6, therefore torque reduction can be prevented from beinggenerated. The same explanation can be applied with respect to otherphase exciting coils. In the case that the motor is driven at a highspeed, a width of the position detecting signal becomes short.Therefore, a DC power source having a high terminal voltage is adoptedso as to shorten the width of building-up portion of the current supplycurve in response to this change.

Furthermore, for example, when the first phase position detecting signal28a is built up, the transistors 20a, 20b are both deactivated. Magneticenergy stored in the exciting coil K is discharged along a path of thediode 21b, the DC power source terminal 2a, 2b, the resistance 22 andthe diode 21a. That is, magnetic energy is returned to the DC powersource. As a result, the exciting current is abruptly reduced. Returnedmagnetic energy is generally stored in a large-capacity rectifyingcapacitor accommodated in the DC power source. Here, a width (shown byan arrow 36a) of a last transition portion of the current supply curve35a becomes shorter as electric power voltage becomes higher. And, ifthe width of the last transition portion does not exceed 30 degrees,substantial counter torque does not occur. The same explanation isapplied to other current supply curves 35b, 35c. In the case that themotor is driven in a high speed region, a width of the positiondetecting signal becomes short. Therefore, a DC power source having ahigh terminal voltage is adopted so as to shorten the width of trailingend portion of the current supply curve in response to this change.

It should be noted that, in the apparatus of the present invention, notonly an allowable maximum rotational speed of the motor can bedetermined in accordance with a voltage value of the DC power source butan output torque of the motor can be controlled in accordance with astandard voltage value applied to the standard voltage input terminal40. That is, the maximum rotational speed and the output torque can becontrolled independently with each other.

A reluctance type motor is different from a DC motor with a magnet rotorin that, as shown in FIG. 6, an output torque is remarkably large when asalient-pole is just positioned to begin entering toward a magnetic polebut is suddenly reduced when the salient-pole begins departing from themagnetic pole. In this case, it is possible to suppress reduction ofoutput torque by supplying the exciting current to the exciting coilsduring a period of time corresponding to a central portion (120 degrees)of a positive torque generation section (180 degrees) shown by an arrow36b in FIG. 6. By this operation, an output torque of the motor becomesflat after a timing B as shown by broken curves 41a to 41c of FIG. 6.However, as the rotational speed of the motor increases, the outputtorque characteristics change from the curve 41a to 41c. Therefore, awidth of the flat torque portion becomes narrow.

Accordingly, in order to further flatten the output torquecharacteristics and preferably advance the exciting current supplytiming so that the exciting current supply operation starts near abuilding-up point of torque curve, installation positions of thedetecting coils 10a to 10c are adjusted so as to gain a flat and largeoutput torque. In the drawing, arrows 36, 36c denote a width of theHIGH-level first phase position detecting signal 29a (120 degrees) and awidth of positive torque range (180 degrees), respectively. Here, if awidth of a trailing end portion of the exciting current curve 35b issmaller than a width of a section shown by an arrow 36d, the countertorque does not occur. The width of the section 36b is twice as large asa width 36a of a trailing edge portion of the section 35b. Therefore, anoutput torque has a long flat portion, and thus, not only ripplecomponent of the output torque can be suppressed within a low level butthe motor can be driven in a high speed region. Furthermore, it ispossible to further extend the flat portion of the torque curve bychanging a shape of the salient-pole of the rotor which faces to themagnetic pole of the armature 16.

The above-mentioned first embodiment can be modified variously.

For example, as shown in FIG. 8, the magnetic poles 16a to 16f and 16a'to 16f' can be formed in a trapezoidal configuration having a short edge(i.e. a tip or distal end) disposed inwardly and a long edge (i.e. abase) disposed outwardly in a radial direction. In this case, mechanicalstrength of the magnetic pole can be increased. Furthermore, even thoughthe distal (or tip) end portion of the magnetic pole is magneticallysaturated, the base portion of the magnetic pole is not saturated withstill keeping magnetically enough room. Thus, the output torque can beincreased much more.

Still further, the number of magnetic poles disposed on the rotor can beincreased. A rotor 1 shown in FIG. 9 is formed with twenty eightmagnetic poles (half of them are indicated in the drawing). In thismanner, if the number of the magnetic poles is increased, there areformed spaces 32a, 32b, 32c, between respective paired two excitingcoils. For example, between the paired exciting coils 16a, 16a' and thepaired exciting coils 16b, 16b' there is formed a space 32a. This spaceis convenient for treatment of terminals of exciting coils and serves asa cooling air passage for cooling down the motor main body.

Moreover, as a detecting object of the detecting coils 10a to 10c, analuminum plate with its outer peripheral portion being formed withprotruding portions instead of salient-poles and synchronously rotatingwith the rotor 1 can be used. Otherwise, instead of a combination of thedetecting coil and the rotor, it is possible to adopt a combination of amagnet rotor synchronously rotating together with the rotor 1 and amagnet resistance element which faces to this magnetic rotor.

Hereinafter, a three-phase half-wave reluctance type motor in accordancewith the second embodiment of the present invention is explained.

The apparatus in accordance with the second embodiment is advantageouscompared with the first embodiment in that it can be operated by a DCpower source having a low terminal voltage such as a battery. Therefore,it is applicable for a power source of an electric automotive vehicle.

A reluctance type motor in accordance with the second embodiment has acurrent supply circuit shown in FIG. 10 instead of the current supplycircuit shown in FIG. 5. This current supply control circuit includes adiode 18 preventing back flow of current and a capacitor 19 instead ofthe operational amplifier 40a and the AND circuits 14a to 14c.

In the same way as the first embodiment, if a HIGH-level positiondetecting signal such as a signal 28a, 29a, and 30a is applied from theposition detecting device to the input terminals 4a to 4c of the currentsupply control circuit, respective phase exciting coils K to M aresuccessively activated to rotate the motor. In this case, the excitingcurrent takes a value obtained by dividing a difference between avoltage applied to the DC power source terminals 2a, 2b and a reverseelectromotive force proportional to the output torque curves 41a to 41dof FIG. 6 by a resistance value of the exciting coil. Therefore, theexciting current becomes substantially constant at the central portionof the current supply section during which the reverse electromotiveforce becomes flat. To the contrary, the exciting current increases at asecond half of the current supply section during which the reverseelectromotive force reduces, thereby increasing an output torque so asto compensate a torque reduction shown in the second half of the outputtorque curve.

Then, for example, if the exciting current to the first phase excitingcoil K is terminated in accordance with last transition of theHIGH-level first position detecting signal 28a, magnetic energy storedin the exciting coil K is discharged via a path consisting of theexciting coil K, the diode 21b, the capacitor 19, and the diode 21a(refer to FIG. 10). Therefore, the capacitor 19 can be charged up to ahigh voltage. As a result, stored magnetic energy is steeplyextinguished and exciting current decreases as shown by a curve 35a(FIG. 6).

In this instance, since the second position detecting signal 29a isalready applied to the input terminal of the current supply controlcircuit to activate the transistors 20c, and 20d, a discharged voltageof the capacitor 19 is applied to the second phase exciting coil L inaddition to the DC power voltage. As a result, the exciting currentflowing in the exciting coil L steeply increases as shown by the curve35b of FIG. 6 and, subsequently, takes substantially the constant valueas previously described. The same explanation can be applied to thethird phase exciting coil M.

Hereupon, as a capacity of the capacitor 19 becomes smaller, respectivewidths of a building-up portion and a trailing end portion becomenarrower. Accordingly, generation of torque reduction and counter torquecan be prevented even if the motor is driven in a high speed region.Thus, the motor can be driven at a high speed with high efficiency.Furthermore, it is possible to remove the capacitor 19 in the case thatone of the paired transistors turn off synchronously at the timing theother paired transistors turn on, where one of the paired transistorsand the other of the paired transistors are associated with excitingcoils of mutually adjacent phases.

The motor in accordance with the present invention is different from thefirst embodiment in that not only return of stored magnetic energy to asmoothing capacitor is prevented by the diode 18 but the stored magneticenergy is successively stored in the exciting coil to be subsequentlyactivated through the capacitor 19 so that charge and discharge ofmagnetic energy can be promptly accomplished between two mutuallyadjacent two exciting coils. Accordingly, a DC power source having a lowoutput voltage can be used.

In the case that the motor in accordance with the present invention hasan output of 500 W and the capacitor 19 has a capacity less than 0.1 fF,a time required for the charge and discharge of the magnetic energybecomes less than 20 fsec and the motor can be driven at a speed of100,000 revolutions per minute. By the way, it is desirable to set thecapacity of the capacitor to be not less than a value capable of surelypreventing generation of counter torque. Furthermore, the back-flowprohibiting diode 18 may be provided to the negative terminal 2b side ofthe DC power source.

What is claimed is:
 1. A three-phase reluctance type motor comprises:afixed armature with three sets of magnetic poles corresponding to first,second, and third phases which are formed on an inner peripheral surfaceof said fixed armature according to a predetermined order, each set ofmagnetic poles including four magnetic poles comprised of a first pairof two adjacent magnetic poles and a second pair of two adjacentmagnetic poles opposing said first pair of two adjacent magnetic polesin a diameter direction of the motor, said fixed armature having aring-shaped core formed with cutouts partitioning a magnetic pathrelating to said first pair of two adjacent pairs of magnetic poles froma magnetic path relating to said second pair of two adjacent magneticpoles; three sets of exciting coils being associated with said threesets of magnetic poles and relating to the first, second, and thirdphases, said three sets of exciting coils being connected with eachother; a rotor rotatably disposed and having an outer peripheral surfaceformed with 26-28 salient-poles disposed at regular intervals, saidpredetermined number exceeding a total number of magnetic poles of saidfixed armature, said first and second pairs of two adjacent magneticpoles being spaced from each other by a distance approximately equal tofour times a width of said salient poles; a position detecting devicesuccessively generating a series of position detecting signals inaccordance with the rotation of said rotor; a current supply controlcircuit connected to a direct-current power source for successivelyactivating said three sets of exciting coils in response to the positiondetecting signals, said current supply control circuit includesswitching elements connected to both ends of said three sets of excitingcoils relating to the first, second and third phases, respectively; andcircuit means for discharging magnetic energy stored in one set ofexciting coils having been just deactivated into another set of excitingcoils to be subsequently activated so that the stored magnetic energycan be promptly extinguished and the exciting current flowing in saidanother set of exciting coils can be greatly increased, said circuitmeans including a diode inversely connected to a connecting unit of anyone set of three exciting coils relating to the first, second and thirdphases and a corresponding one of said switching elements, said storedmagnetic energy being discharged through said inversely connected diodeinto said another set of exciting coils.
 2. A three-phase reluctancetype motor in accordance with claim 1 in which said set of adjacent twomagnetic poles are disposed to be spaced over a distance equal to asection wherein three salient-poles are arrayed.
 3. A three-phasereluctance type motor in accordance with claim 1 in which each of saidmagnetic poles has the same circumferential width and each of saidsalient-poles has the same circumferential width.
 4. A three-phasereluctance type motor in accordance with claim 3 in which saidcircumferential width of the magnetic pole is identical with saidcircumferential width of the salient-pole.
 5. A three-phase reluctancetype motor in accordance with claim 1 in which said magnetic poles arerespectively formed in a trapezoidal configuration to have a baseportion wider than a distal end portion in a circumferential direction.6. A three-phase reluctance type motor in accordance with claim 1 inwhich magnetic poles relating to said second phase are formed spaced bya mechanical angle of 60 degrees from a respectively corresponding oneof said magnetic poles relating to said first phase, and said magneticpoles relating to said third phase are formed to be spaced by amechanical angle of 60 degrees from respectively corresponding ones ofsaid magnetic poles relating to said second phase.
 7. A three-phasereluctance type motor in accordance with claim 1 in which said positiondetecting device successively generates the position detecting signalscontinuously without overlapping with each other, and each positiondetecting signal has a width of an electrical angle of 120 degrees.
 8. Athree-phase reluctance type motor in accordance with claim 1, furthercomprising a back-flow prohibiting diode interposed in a direction ofeasy flow with respect to said direct-current power source, when one ofsuccessively generated position detecting signals is extinguished andanother one of the position detecting signals is newly generated,magnetic energy stored in an exciting coil relating to said one positiondetecting signal can be prevented from returning to the direct-currentpower source by said back-flow prohibiting diode, and further saidmagnetic energy can be promptly transferred into magnetic energy storedin an exciting coil relating to another position detecting signal,thereby minimizing torque reduction and counter torque generation.